Sonic Robo Blast 2

Sonic Robo Blast 2 (or SRB2 for short) is a fan made, free themed game using a modified version of the Doom engine, based on Doom Legacy. The game focuses on recreating the feel of the classic 2D Sonic games. As of 2023, the latest version of the game is version 2.2.13. It is not yet complete, as some acts of zones are missing, and Dark City is only at the conceptual stage.

Engine
While the engine is derived from Doom Legacy, which was originally chosen for its 3D floors, it has greatly diverged and been extended in different directions.
 * The original Doom games are no longer supported. FraggleScript has been removed as well.
 * New 3D floor types, such as intangible from one side, crumbling a few seconds after a player lands on them, Quicksand, Shatter Blocks and Custom 3D Floors allowing combination of built-in 3D Floor effects, among others
 * Polyobjects with additional effects allowing to create moving platforms. They can now render flats, carry players standing on them, follow waypoints, and can have sector specials applied to them.
 * ANIMDEFS
 * Lua scripting
 * Custom "SOC" (Sonic Object Configuration) content definition language
 * Partial support for ZDoom's TEXTURES lump
 * Camera effects
 * Skins extended to full-fledged character classes
 * Slopes with Classic Sonic styled physics. 3D floor slopes, vertex-based slopes and dynamic slopes are all supported in both Software and OpenGL Renderers.
 * Reverse gravity and Scale actors ingame, works on both Software and OpenGL Renderers.
 * v2.1.21 added PK3 support to help reduce file size and improve organization of resources through subfolders.
 * v2.2.11 added UDMF support and removed the framerate limit of 35 fps.

Gameplay
In SRB2, players run at high speeds through generally light-hearted, happy levels (though some exceptions do exist, such as Castle Eggman Zone), in comparison to the usually dark and dim battlefields of Doom levels. Players jump at heights unprecedented in Doom, achieving heights of 124 fracunits. Players are additionally equipped with a spindash, which can be charged up using the spin button. Players encounter badniks in the field, that can be destroyed by jumping on them once, as opposed to the hellspawn of Doom which require several shots to be slaughtered. After two acts of gameplay, players encounter a third act of gameplay in which they find a boss, who must be defeated to finish the level. In boss acts, an egg capsule rises out of the ground for the player to jump on, and finish the act. However, not all boss acts feature an egg capsule, and end the level shortly after defeated. The latest version of Sonic Robo Blast 2 has seven different zones, though some still not yet complete.

At the character select screen, players choose between one of three characters: Sonic, Tails, or Knuckles. While Tails and Knuckles have mid-air abilities that resemble their previous appearances (Flying and Gliding/Climbing, respectively), Sonic has an ability reminiscent to the Jump Dash in Sonic games: the thok. Upon using the ability, Sonic shoots forward with a massive burst of speed. This gives Sonic a massive advantage in multiplayer modes such as race, and also in single-player time attack.

In addition, special stages are included and allow the player to collect chaos emeralds. When the player finds an emerald token in a level, they will be taken to a special stage after finishing the level. The special stages are based on the game . In these stages, the player flies along a curved 2D track as Super Sonic and has to collect a certain number of blue spheres and finish the stage before time runs out to obtain a chaos emerald.

After collecting all the chaos emeralds, Sonic obtains the ability to turn into Super Sonic. Players turn into their super form by using their mid-air ability with 50 rings and no shield. When the player is in their Super form, they can jump higher than before, as well as run faster, even on water. Sonic has the ability to float in mid-air when the player presses and holds the spin button in air. While in Super Form, the player is constantly drained of rings. After the player loses all of their rings, the player turns back into their normal state, with normal jump height, speed, and loses their ability to run on water and float.

Levels
These levels are current as of v2.2.13.

Single-Player
Greenflower Zone - A grassy area filled with rivers, small trees, and flowers. Act 1 is a rather short level which introduces the player to the basics of the game. Act 2 takes place at the bottom of large canyons, and also features large rivers, waterfalls, and caves. The boss of Greenflower Zone simply fires a laser. After five hits, he will spawn 3 lasers instead of 1 at a slight faster speed while slowly tracking to the player.

Techno Hill Zone - Eggman's presence in this area has altered the landscape. Most noticeably, he's filled low lying areas with buoyant slime, which will cause the player to move slowly, and anything that enters it is slowly pushed back upwards towards the surface. Act 1 takes place outside and in the entrance to one of Eggman's factories. Act 2 takes place in the heart of the factory and has lasers, conveyor belts, crushers and turrets. The boss flies in a circular pattern while spewing small puddles of slime. After five hits, the boss bounces at the player and spews slime into a circular pattern with each bounce, and attempts to " stomp" the player.

Deep Sea Zone - As the name would imply, this zone is set largely underwater. Remain there for 20 seconds, wait for the countdown to go all the way to 0 and the player will drown. However, the countdown can be reset by grabbing large air bubbles as they emerge from the ground. Other hazards include collapsing ruins, waterslides, and underwater currents. In addition, there are puzzles involving pushable stone gargoyles, which often led to rewards. The boss here emerges from one of five chutes and tries to shoot the player. If the player falls into the water below, they'll be electrified a short time later. After five hits, invulnerable, inflatable Eggman clones will appear and start emerging from the chutes simultaneously, and will shoot at you along with the original.

Castle Eggman Zone - Takes place in the rather gloomy medieval fortress under Eggman's care. Swings will propel you ahead and above, but watch out for swirling maces, cannonballs, and flamethrowers. Act 1 takes place in the forests and gardens on the property, while Act 2 covers the chambers and grounds of the titular castle. Its boss has a 3D floor based cage that it uses to protect itself while swinging around long strings of maces to hit you.

Arid Canyon Zone - This rather scenic and rugged canyon is accented with cacti, tumbleweeds and the occasional oasis. Moving cables will give you a lift over precarious ground. Jump quickly to escape quicksand and pools of oil. Watch out for rockslides, open fissures, and slippery oil slicks.

Red Volcano Zone - The lava in this expansive subterranean cavern is prone to rising without warning, so watch out. Other things to be wary of include series of collapsing platforms and jumping fireballs. Red Volcano Zone has one act and no boss.

Egg Rock Zone - The player finally makes it to Eggman's extraterrestrial headquarters planted firmly on the energy-filled Black Rock. This zone features many of the previous levels' hazards and gimmicks, and adds inverted gravity (which can be triggered by the player sometimes, and sometimes not), air locks, and short sections in airless vacuums. Remain oxygen-free for too long, and you'll suffocate. Act 2 is also features brief 2D sections.

Black Core Zone - Includes a race and fight with Metal Sonic, and an Eggman fight based loosely on the cyberdemon and arch-vile.

Pipe Towers Zone - A tribute to the original Super Mario Brothers, with Goombas, Koopa shells, coins, and item-filled boxes. The first half of the level takes place in the overworld and through systems of pipes and bouncy mushrooms, and the second half is based off of the underground levels with moving platforms and Thwomps. The level ends with a 3D recreation of the end-level castle. Pipe Towers Zone has one act and no boss.

Haunted Heights Zone - The first challenge stage, which is unlocked by completing the main story. This industrial Halloween themed level adds several new thematically appropriate gimmicks such as player slowing spider webs and themed enemies such as a pumpkin shooting Cacodemon. Haunted Heights Zone features one act and no boss.

Aerial Garden Zone - A challenge level set on a picturesque floating temple. This level is unlocked by beating Haunted Heights Zone, the first challenge level. The name of the game here is risky platforming over an unforgivable and vast bottomless pit. Activate panels (some of which must be warped to) to open doors and progress further. Aerial Garden Zone originally had four acts that were eventually combined into one and features no boss. Special Fact: Aerial Garden Zone was based off a SRB2 add-on created in the final demo era called Mystic Levels, later renamed as Mystic Realm.

Azure Temple Zone - Another challenge level, Azure Temple Zone is set entirely underwater and is unlocked by beating Aerial garden Zone. Sonic Robo Blast 2's slower movement in water and air management can be negated by finding one of several air bubbles placed throughout the level. Azure Temple Zone features one act and no boss.

Later editions of Sonic Robo Blast 2 will feature additional levels, bosses, and other content.

Multiplayer
SRB2 supports numerous multiplayer modes, some of them sporting first-person gameplay, while others featuring more Sonic-like gameplay. There exists an online mode based off Doomseeker's method of a master server. Also there is a 2-player Sonic The Hedgehog 2 split-screen based mode with no multiple PC nor server requirements.

Co-op
SRB2 supports a Cooperative mode, in which many players can complete a level together. The levels proceed normally, and after one player (or all, depending on settings) completes the level, the stage ends.

Competition
This mode is a variation of Sonic 2's multiplayer split-screen mechanics. There are five different requirements: score, time, ring count upon finishing the map, total number of collected rings and number of popped monitors. Players receive points based on how well they were in each of the five categories (e.g. the player with the most total number of collected rings receives points equal to the number of players currently playing). The winner is based upon who has the most overall points at the end of the level.

Race
In this mode the winner is based upon who finishes first, or Time is the only factor counted for the winner, as opposed to the points system installed in Competition. 60 seconds after the first player finishes, all players that have not finished run out of time and die. As for completing the levels, two systems exist: normal and circuit. The first type of racing is much like any typical race: the first one to finish wins. The other type, circuit, requires the player to finish a number of laps around a course. The number of laps is specified by the server.

Match
Players chuck rings at each other. Rings draw ammo from the player's ring count, and thus the player must conserve ammunition. Also, an interesting twist is that a player loses all of his rings (which are also ammo) after being hit. The player is given invincible time to collect spilled rings, or just plain rings. When the match ends, the player with the most points wins. As of version 2.0, a new Match system has been coded, along with Tails and Knuckles' super forms, only available in Match or CTF.

Tag
Players either shoot rings at each other, or touch each other to pass on the "it" status, depending on whether Tails pickup ON or OFF. Characters who are not "it" lose their special jumping ability in order to give the person who is "it" a fair advantage. Points are earned if one player can avoid being tagged if the "it" status is given to another player. An additional variant of this game mode called Hide and Seek exists as well, which stops non-"it" players from moving after a set period of time.

Capture the flag
In Capture the Flag, players attempt to capture the opponent team's flag. Players are assigned to teams automatically after exiting spectate, and can also switch mid-game. Afterwards, players must try to capture the enemy flag. Both flags must be at a base in order to score a point. The player loses use of their mid-air ability when carrying the flag.

Modding and add-ons
Sonic Robo Blast 2 has accumulated a substantial community, which is dedicated to creating several add-ons for the game. Custom maps are generally created using an editor called Zone Builder, itself a fork of GZDoom Builder. Due to SRB2's origins as a fork of Doom Legacy, many aspects of level building will be immediately familiar to Doom mappers. The game has Lua support, and a language for a new file type called Sonic Object Configuration, or soc. The formats used are .soc for the latter, whereas Lua scripting files are stored as .lua files.

New characters and levels can be added by entering the console (by pressing the key ¬ or `) and typing the following without the quotes: "ADDFILE EXAMPLE.WAD" or "ADDFILE EXAMPLE.PK3". Simply press enter to execute the command, or add the WADs via a launcher by going to the WAD files section and adding them there. SRB2 v2.1x and v2.2x features a graphical interface for loading add-ons as well. Later builds of v2.1 have also added .pk3 support for compressed modding.